A virus-neutralization test for infectious laryngotracheitis virus was performed in microtiter plates using standard techniques. To assess the reproducibility of the test, 11 sera were each titrated repeatedly once a week for 8 weeks, and the results were compared to a standard. The standard used for reproducibility was that the 95% logarithmic confidence intervals of the mean calculated from three titrations of the same serum had to be smaller than the logarithmic distance "within" two microtiter plate wells. For the virus neutralization test to give reproducible results, such confidence intervals had to fall "within" two wells at least 75% of the time. Over the 8 weeks, percent reproducibility varied from 43.5% to 81.5%. The infectious laryngotracheitis virus-neutralization test did not meet our defined standard of reproducibility with positive antisera. Results with negative control sera were reproducible, however. Percent reproducibility varied from 31.8% to 93.8% for different sera tested, but it was not related to the titer of the sera.